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MG Midget and Sprite Technical - Lever Arm Damper Tuning (Valves and Springs)

I have never been entirely satisfied with the ride/handling of the rear of my car. So whilst underneath I decided to remove the dampers and give them a clean out and some fresh oil. A cheap thing to try first.

I removed the valve assemblies from both and noticed they were slightly different (see attached). The spring looks stronger on one of them, as well as the shoulder (arrowed) being larger.

Anyone have any experience messing with the valves and springs? I am pondering the implications of the differences and whether to go to the effort of matching them.

I did find this but have yet to digest it fully:

https://sites.google.com/site/morganatica/suspension/armstrong-lever-arm-dampers---adjustment

Cheers,
Malcolm.


Malcolm Le Chevalier

At one time, the slick trick was to silver solder two of the four holes in the valve body to restrict the oil flow. I never tried it so I can't comment on results. Maybe someone here has experimented with this.
J Bubela

I have always thought the arrangement was intended to be progressive, such that under light or slower movement of the suspension, oil would flow through the small holes. Then if the displacement was more rapid the oil valve would lift off its seat as the spring compressed. I thought the design was to stop the damper locking solid when you hit a bigger bump, and maybe to stop the damper body from splitting asunder in extreme cases.

I never spotted the differences between the front and rear valve assembly, but then I didn't look that close. The only "upgrading I have ever done is to experiment with different viscosity oils, as many others have tried.
GuyW

I attach copies of the Armstrong brochure I have which may be of interest


Doug Plumb

page 2


Doug Plumb

page 3


Doug Plumb

page 4


Doug Plumb

Thanks Doug. The valves are from the two rear dampers, in case you were confused Guy.

Found a how it works article on an MGA site which has explained a lot.

Cheers
Malc.
Malcolm Le Chevalier

That's great, Doug.

Malcolm

Link please?
Dave O'Neill 2

As the dampers are handed, do you think it's likely that the damping rates are different to compensate for other factors such as driver weight, torque reaction of the axle &c? I don't know if they are but in such a light car it seems at least plausible to me.
The photo shows the rebound control poppets and springs. Are the compression parts different too?

The web page you posted appears to show a damper valve from a Morgan which differs somewhat to the arrangement shown in the document posted by Doug.

Maybe a PO has replaced a damper or dampers with mismatched units, which would explain your unease about the handling. Similar units were used on lots of different cars (and vans), so it could have been done in error.

By the way Moss still list new units as well as recon. No idea if they're any good or if they're Asian repros but they might know if the damping rates are different. Just a thought.

http://www.moss-europe.co.uk/shop-by-model/mg/midget/steering-suspension/rear-suspension/rear-suspension-midget-iii-sprite-iv-midget-1500.html

Thanks for a very interesting Q.

Edit: crossed in the post with Dave and Malcolm.
Greybeard

And don't rule out reconditioned ones being supplied in the past which were taken off the shelf as a mismatched pair because no one had actually opened them up to check!

Maybe the 4 hole version was for a softer sprung 1500?
GuyW

Malcolm

I did similar to all 4 last year. The link you have is most informative and there is other useful info out there on the interweb. I did not mess around with the springs or valves, and to be honest I too cannot recall if there were any differences. Good spot though, and I would be tempted to try match them if at all possible.

I simply replaced O rings etc. with a reconditioning kit. I did though replace the metalastic bushes on the links, and replaced the oil with Silkolene Motobike fork oil - IRRC SAE 30 - which (allegedly) compensates for any wear in the pistons/bores and gives a slightly firmer damping response. Whilst you are there, check the damper body mounting bolts are firstly all present(!) and secondly correctly torqued.

Well worth it. A noticeable improvement in handling for little cost and effort.
Oggers

Link to MGA site about workings of the armstrong dampers:

http://mgaguru.com/mgtech/suspensn/fs119.htm

They are pretty simple in operation really.

The dampers are recon units, so history and origin is completely unknown. When I bought them, I was young and stupid and thought the big boys would better know what they are doing than I would... Yeah right :-)

I suspect the bottom one (in pic above) is a reproduction valve assembly, or maybe an "uprated" assembly. I noticed just now that it doesn't have this little nick in it (attached pic, red arrow).

Due to it's position it would act in both directions (piston seating areas blue arrows) allowing greater flow for smaller valve movements.

I am going to have a more considered back to back play with the two dampers this evening.

Malcolm.
Malcolm Le Chevalier

Pic. Sorry.


Malcolm Le Chevalier

Bit more of a look see just now.

For the sake of discussion, damper A appears to be genuine Armstrong. That is the top valve in pic one, the one also with a nick in it.

The other, damper B, I think is a poor repro. It does not have any Armstrong markings on the casing.

Another difference of B is the valve "cap" has 4 holes in instead of two on A and doesn't have an o ring to seal off the bump and rebound circuits. Compare the attached to pics at the two links.

Cheers
Malc.
Malcolm Le Chevalier

Again, sorry, Pic.

In terms of response when moving them by hand. B feels stiffer and notchier and sometimes would lock up completely in one direction (well, locked so much as I couldn't move it by hand with it clamped in a vice). Pretty rubbish really.

EDIT: Reading Dougs info. Pic three. The "nick" is labelled as the bleed groove. Cheers Doug. Learning a lot here.


Malcolm Le Chevalier

Malcolm,

Peter May offers re-valved dampers so he may be open to an approach to buying 4 valves?

Jeremy T2

Peter doesn't do them himself, he farms them out so supplying parts might not be possible. Worth asking though!
David Smith

Malcolm,

"I have never been entirely satisfied with the ride/handling of the rear of my car." What do you mean? sliding? driving as on waves? to quick entering corners?
The back axle of a Spridget should be sparsely damped. And a worn out Armstrong is perfect. (See Caroll Smith: tune to win and drive to win)

3 different bump and 3 different rebound springs exist. Yes it is better to match them. You can do that with the springs or with washers (bump). The nut is for rebound. Rebound should be 3 times stiffer than bump. You can test it on a special tool.(expensive). Or on the road.

Armstrongs always wear on the level arm axis (no bearing!) and the pistons. The pisons always move over the same 3-4 mm. As the arm piston ratio is 10:1.




Flip Brühl

Oggers

Where did you get the recon kit - I have a number of units that I think only need O rings
Dominic Clancy

Dominic

Unfortunately, I simply cannot remember. On reflection, I may simply have obtained new O-rings from a local hardware shop. IIRC, they are industrial sizes and fairly commonplace.
Oggers

This thread was discussed between 12/01/2017 and 16/01/2017

MG Midget and Sprite Technical index

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